1. Field of the invention
The present invention relates to corrosion resistant Al or Al alloy materials which are coated with a deposit of multilayer structures. These Al or Al alloy materials are useful as components for devices, appliances and equipments of which a high level of reliability is required.
2. Description of the prior art
Al or Al alloy materials are lightweight and possess fairly good strength and corrosion resistance, and also possess excellent workability and electrical properties. Hence, Al or Al alloy materials have found extensive applications as construction materials, automobile wheels and body panels, canning materials and various metallic containers, and further in the electronics field. Despite these advantages, however, it is known that on these Al or Al alloy materials take place corrosions, representative of which is pitting, under acid or alkaline environments, or even under neutral environments where chloride ions and other halogen ions are present. These corrosions cause serious damage to any devices, appliances or equipment which use Al alloy materials as their component material, substantially impairing the reliability thereof.
For instance, in Al conductor materials which are used in semiconductor devices, with the recent trends toward the increasing integration and density of these devices, the materials have become increasingly finer and thinner. This has brought much more attentions to the problem of corrosion resistance. Especially in Al conductor materials that are employed in silicon LSI currently under research and development when an age of submicron is now being entered the ones as fine and thin as approx 1 .mu.m wide are required. As LSI has become more integrated, the plastic package layer which is used as protective material has not only become smaller and thinner, but they have become more exposed to excessive stress and severe corrosive environments as a result of a production process with higher production efficiency. Much higher degree of reliability of conductor materials against corrosion, as well as their reliability against electromigration and stress migration, has been required than ever before.
Incidentally, the conventional semiconductor devices are housed in a plastic package in order to prevent the penetration of moisture from the atmosphere and avoid deterioration due to oxidation. On the plastic package, various studies about passivation refinement technology have been under way, including the improvement of resin materials.
When a plastic package is used, a direct contact between device and resin is structurally unavoidable. Accordingly, various problems occur which arise from the properties peculiar to the resin comprising the plastic package. Most of the resin, for example, possesses moisture permeability and hygroscopicity, and also contains substances which are easily ionized in the presence of water, such as chloride and sodium, al though in small amounts. There are many defects, including pin holes, and when they are stored or used in an atmosphere with high temperatures and high humidities, moisture penetrates thereinto in a diffusive fashion, and condensates inside the package, causing corrosion of Al conductor materials in semiconductor devices.
To overcome this problem, methods have been proposed in which the corrosive resistance of Al conductor materials themselves are improved by forming passivation coating (SiO.sub.2 protective coating) on the surface of Al conductor materials. In a passivation film of single layer structure, however, not al of the pin holes, cracks and other defects can be eliminated no matter how coating materials or coating producing procedures are devised. Moisture and other substances which penetrate through these defects into the package corrode the Al conductor materials, until they are broken. To improve the corrosion resistance, anti-migration property and other reliabilities of the Al materials themselves, methods are proposed in which some 1 to 2 wt % silicon is added to the Al materials, or similar amounts of silicon and about 0.5 to 4 wt % of Cu are added thereto in a combined manner. These methods have proved not to give satisfactory corrosion resistance to the Al materials.